How to make Java work with SQL Server?
Do not put both the old sqljdbc.jar and the new sqljdbc4.jar in your classpath - this will make it (more or less) unpredictable which classes are being used, if both of those JARs contain classes with the same qualified names.
You said you put sqljdbc4.jar in your classpath - did you remove the old sqljdbc.jar from the classpath? You said "it didn't work", what does that mean exactly? Are you sure you don't still have the old JAR in your classpath somewhere (maybe not explicitly)?
The driver you are using is the MS SQL server 2008 driver (sqljdbc4.jar). As stated in the MSDN page it requires Java 6+ to work.
http://msdn.microsoft.com/en-us/library/ms378526.aspx
sqljdbc4.jar class library requires a Java Runtime Environment (JRE) of version 6.0 or later.
I'd suggest using the 2005 driver which I beleive is in (sqljdbc.jar) or as Oxbow_Lakes says try the jTDS driver (http://jtds.sourceforge.net/).